“In short,” the report says, “spending — and saving — among American consumers is changing, and not necessarily for the better.”

The U.S. saving rate is a fraction of what it used to be: 4.6 percent today versus 13 percent four decades ago, according to the report.

“Where are we putting the extra money? Not into retirement accounts, stocks or bonds, clearly,” the report says. “The 1973 households surveyed are still more or less in decent financial standing today; we’ll see how it works out for those of 2012.”

The analysis provides an interesting snapshot of American spending habits.

In 1973, according to ConvergEx, the average American had post-tax income of $9,700. Annual spending was $8,270, or 85 percent of income.

Income has risen to about $63,000 today, but per-person expenditures average only 81.2 percent.

That may seem counterintuitive given that smartphones, Internet access and ubiquitous pay TV didn’t exist in the era of Watergate and the Arab oil embargo.

Americans spend about the same percentage on phone service today (2.4 percent) as they did in 1973 (2.2 percent), according to the report. Phone companies have raised cellular rates, but that’s been offset by consumers scrapping their land lines.

Overall housing costs have risen to 32.8 percent of income from 30.8 percent.

But the cost of so-called shelter, an owned or rented dwelling, has jumped to 19.2 percent from 15.9 percent. That’s due partly to an increase in average home size, to 2,700 square feet from 1,400 square feet in 1970.

A notable cost reduction has come in food, according to the report.

The average family shells out 12.8 percent at grocery stores and restaurants today, versus 19.3 percent in 1973. Smaller average family size — 2.5 people today versus 2.9 people in 1973 — explains part but not all of the difference.

Overall spending on transportation has fallen to 17.5 percent today from 19.3 percent in 1973, as vehicle purchases and expenses have declined to 6.6 percent from 9.5 percent.

But the cost of gas and motor oil has increased notably. It’s at 5.4 percent today from an elevated 4.2 percent during the 1973 oil crisis.

One surprising cost-saving: “floor coverings,” which went from 0.5 percent in 1973 to nothing today. How to explain it? “The death of the shag carpet,” Millar surmises in the report.